Abstract: The direct effects of black carbon (BC) aerosols over China on East Asian summer monsoon have been investigated using the latest version of general circulation model (GCM) CAM3.0 developed by NCAR/UCAR, which is coupled with an off-line aerosol assimilation system. The model results show that BC aerosols over China can bring about a global average radiative forcing of 0.13 W/m2, resulting in the decrease of land surface temperature in most of China except for Qinghai, Tibet and Guangxi provinces where the surface temperature increased. Therefore, the differences in surface temperature and pressure between land and sea reduce, which finally weakens East Asian summer monsoon. BC aerosols have less effect on weakening monsoon intensity compared with sulfate aerosols. However, it increases precipitation, especially convective precipitation in the middle and lower reaches of the Yangtze River. On the contrary to sulfate aerosols, BC aerosols enhance the convective activities in the southeast of China. Besides, the joint effect of BC and sulfate aerosols over China has also been studied. The model results indicate that the synthetic effect of sulfate and BC aerosols is similar to that of sulfate aerosols only, and precipitation changes induced by the joint effect are also consistent with those by the sulfate aerosols effect.

Key words: black carbon aerosols, sulfate aerosols, East Asian summer monsoon, convective activity